Spectra by the Thousands

The best way to get good at interpreting spectra is by experience. Look at as many spectra and do as many spectroscopy problems as you can. 

The other is the Organic Structure Elucidation workbook, created by Professor Bradley D. Smith (Notre Dame)  

WebSpectra includes 75 problems. All the problems display the and C spectra, several with DEPT or COSY enhancements. A number include IR spectra. Organic Structure Elucidation contains 64 problems, all with and C NMR, IR, and mass spectra. The exercises in both WebSpectra an6 Organic Structure Elucidation are graded according to difficulty. Give them a try. 

Vast numbers of NMR, IR, and mass spectra are freely accessible via the Spectral Data Base System (SDBS) maintained by the Japanese National Institute of Advanced Industrial Science and Technology at  

The SDBS contains 14,800 NMR, 13,100 C NMR, 51,600 IR, and 24,200 mass spectra. Not only does the SDBS contain more spectra than anyone could possibly browse through, it incorporates some very useful search features. If you want spectra for a particular compound, entering the name of the compound calls up links to its spectra, which can then be displayed. If you don t know what the compound is, but know one or more of the following  

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Ring Currents Aromatic and Antiaromatic Magnetic Resonance Imaging Spectra by the Thousands Gas Chromatography GC/MS and MS/MS... 

Chapter 13 Spectroscopy has been supple mented by an expanded discussion of H and C chemical shifts and a new section on 2D NMR A new box Spectra by the Thousands points the way to websites that feature libraries of spectra and spectroscopic problems of every range of difficulty... 

Ring Currents Aromatic and Antiaromatic Spectra by the Thousands... 

Spectra by the Thousands 575 Infrared Spectra 576 Characteristic Absorption Frequencies Ultraviolet-Visible (UV-VIS) Spectroscopy Mass Spectrometry 584 Molecular Formula as a Clue to Structure 589 Summary 590 Problems 593... 

Ring Currents Aromatic and Antiaromatic 551 Magnetic Resonance Imaging (MRI) 564 Spectra by the Thousands 575... 

Although individual laboratories find it useful to compile their own reference library files, access to very large collections of mass spectra and to published data [55] is essential. A compilation of many thousands of spectra by the Aldermaston Mass Spectrometry Data Centre and the Division of Computer Research and Technology at the National Institutes of Health [56-58] has been made available commercially. The file can be searched in a number of ways using an interactive conversational mass spectral search system via a teletype and acoustic link over telephone lines. 

Idenlihcaiion of a species from iis mass spectrum involves a search of files of spectra for pure compounds until a match is found done manually, this process is lime consuming, but it can be accomplished quickly by using a computer. Here, the spectra of pure compounds, stored on a hard disk, are searched until spectra are found that arc sintilar to the analyte. Several thousand spectra can be scanned in a minute or less. Such a search usually produce.s several possible-compounds. Further comparison of the spectra by the scientist often makes identification possible. 

The microcomputer should incorporate a VDU and have high-density colour graphics capability (up to 1760(x) x 1280(y)). This enables IR-spectra to be displayed on the screen of the VDU with excellent definition so that comparisons, the results of scale expansions and other spectral manipulations can immediately be seen. Parameters such as range, scan time, data point interval, etc., are set and monitored under microprocessor control and stored along with the spectrum. During the scanning of a sample, several thousand data points may be collected and stored in RAM which should be able to accommodate and display at least three spectra simultaneously. There is a wide range of manipulations that can be performed by the analyst on stored spectra, e.g. 

Mass spectrometers are among the most selective detectors, but they are still susceptible to interferences. Isomers have identical spectra, whereas many other compounds have similar mass spectra. Heavy petroleum products can contain thousands of major components that are not resolved by the gas chromatograph. As a result, multiple compounds enter the mass spectrometer simultaneously. Different compounds may share many of the same ions, confusing the identification process. The probability of misidentiflcation is high in complex mixtures such as petroleum products. 

The experimental evidences for these conclusions derive mainly from low-temperature spectra of isolated molecules in rigid matrices.62,63 The diffuseness observed ranges from a few tenths of a cm-1 to thousands of cm-1. In the case of a relatively simple molecule like naphthalene that has two nearby states (S at 31,680 cm-1, and S2 at 34,420 cm-1) a careful study of the second state shows many relatively sharp lines emerging from a diffuse background.64,65 It appears that these sharp transitions can be associated with vibrational levels of the lower electronic state, and that the intensity is borrowed from the second state by the mixing of vibronic states having different electronic parentage in the Born-Oppenheimer representation. 

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